Vehicles are frequently employed in underground environments such as mines for transporting personnel and equipment, or to serve as a mobile platform for relatively light equipment, such as a lift to allow personnel to string electrical cables or otherwise work in an elevated position. Because these underground environments feature uneven terrain and rough rock walls, such vehicles are typically subject to severe wear and susceptibility to damage. This is especially true of vehicle bodies, which are classically formed of much thinner material than that which makes up the rigid frame of the vehicle; such bodies are easily damaged by impact with rock surfaces. To counter this, it is desirable for such vehicles to be built with a more rigid and durable structure than conventional vehicles intended for road travel, and to have a suspension system which can withstand the rigors of heavy use on uneven surfaces.
One early patent addressing the issue of durability for a vehicle is U.S. Pat. No. 1,554,167, which teaches a truck frame assembled from components including two U-shaped channel side pieces which are taught as providing buffing surfaces to allow the vehicle to be used in narrow spaces.
More recently, vehicles have been made with a structure where the frame of the vehicle is unitized with the body and the body is fabricated from metal plate stock. While such vehicles have been found to have the desired durability when operated in underground environments, the unitized structure may be too large to pass through sections of the mine where the path is constricted, in particular the entrance passage, which is frequently limited in size. In some cases, this has required a vehicle to be cut into sections to pass through these constrictions so as to be introduced into the work site in the mine, and the sections then welded back together. This process would need to be repeated to move the vehicle to a new work site.
Another concern with the use of unitized construction for a mine vehicle is that it limits the ability to readily configure the vehicle for different purposes. Because mine vehicles may be needed for various uses, it is desirable to employ a design which can be readily adapted to various configurations. For over-the-road vehicles, this problem has been partially addressed in the trucking industry by providing telescoping frames and repositionable wheels, such as taught respectively in U.S. Pat. Nos. 6,199,894 and 5,720,489. However, such structures result in reduced strength when expanded and/or result in larger subassemblies when disassembled. Also, such a solution does not readily lend itself to interchangeability of parts, which could simplify fabrication of different vehicles by allowing the use of more standardized parts; the use of interchangeable parts might also allow a particular vehicle to be reconfigured for a different use as the needs of the user change.
Another problem in underground environments can be the unevenness of the terrain over which the vehicle is operated. One approach to effectively deal with the changes in the inclination of the mine floor and manipulating the vehicle in a mine environment is to provide a durable and forgiving suspension system. For trailers used in the transporting industry, one durable type of suspension which has been employed in over-the-road vehicles has been to use a “trunnion axle suspension”, which employs trailing arms to which an axle is mounted, each of the arms being pivotably connected by an axle to the vehicle frame at a point ahead of the axle. In some cases this can be done by employing an elastomer bearing at the point of articulation to accommodate very limited movement and reduce wear. One or more shock-absorbing elements are connected between each of the arms and the frame, either ahead of or to the rear of the axle; the trunnion axle suspension is particularly well suited for use with an air spring as a shock-absorbing element. Typical examples of such suspensions are illustrated in U.S. Pat. Nos. RE 30,308; 3,332,701; and 6,550,795; and in U.S. Publication No. 2003/0020251. These mechanisms generally have fixed pivot shafts about which the trailing arms rotate. These pivot shafts are either fixed to the frame to which the arm is mounted or, alternatively, are formed as part of the trailing arm. In either case, these structures provide minimal transverse motion of the arm; this limited motion may be adequate for many road conditions, but will not serve well when traversing more challenging surfaces, since these devices essentially limit the motion of the trailing arm on which the axle is mounted to motion in a plane to which the axis of the pivot shaft is perpendicular.
Thus, there is a need for a vehicle structure which is sturdy yet which can be readily disassembled into smaller components and which can be readily configured for various uses. There is also a need for a vehicle suspension system which is durable and well suited for use supporting a driven axle when the vehicle is operated on uneven terrain.